In the field of oil and gas well abandonments there are issues arising in the measurement and remediation of surface casing vent flows (SCVF), which primarily consist of methane emissions. Taking Alberta, Canada as an example, the Alberta Energy Regulator (AER) statistics from 2013, state that a total of 430,000 wells have been drilled in Alberta. Of those, 151,000 have been abandoned. This leaves 279,000 producing or suspended wells to which testing and monitoring SCVF regulations for venting methane emissions apply. The occurrence of active SCVF ranges upwards to 18% of this well count, representing just over 50,000 wells leaking fugitive methane emissions to the atmosphere. The other two provinces of British Columbia and Saskatchewan combined, would represent an additional 40% of the Alberta estimates.
The Alberta Energy Regulator (AER) regulations state that all producing, shut-in, and inactive wells must be inspected and SCVF (Surface Casing Vent Flow) tested on a regular basis. All wells to be abandoned must be SCVF tested upon commencing abandonment operations and prior to cutting and capping for reclamation.
Additionally, on average a range of 6,000-18,000 wells are drilled in any one-year in Alberta. The Alberta Energy Regulator (AER) dictates that all newly drilled wells must to be SCVF tested and reported within 90 days of rig release.
The Alberta Energy Regulator (AER) has a recommended procedure for the above testing operation for the measurement of oil and gas well surface casing vent flows (SCVF) as outlined in AER Well Abandonment Directive 20 and Interim Directive ID 2003-01
A “bubble test” is currently used to measure fugitive gas emissions from an oil and gas well casing vents. Fittings are attached to the surface casing vent and either a ¼″ (0.635 mm) or ½″ (12.7 mm) tube is placed into 1″ (25.4 mm) of water in a bottle, an on-site operator watches the bottle and tries to count the bubbles that occur within the 10 minute regulatory period. There are many reasons why this method may give inaccurate flow results: different size tubes cause different bubble volumes; operator subjectivity in what constitutes a bubble; too many bubbles to count; intermittent emissions may not be present during the timeframe; no determination if the bubble is air or hydrocarbon; and the most important deficiency is the lack of a direct and accurate measurement to qualify and quantify flow rate for these fugitive emissions. Neither does Industry currently have the technology to establish a scientifically proven baseline for fugitive methane emissions to the atmosphere.